This invention is related to continuous flow centrifugal separation of blood, and in particular, to an improved centrifuge assembly utilizing a disposable blood container. The prior art is replete with a number of concepts for separating the components of blood utilizing complex channeling or grooves in the centrifuge bowl together with fluid connections for input/output functions. Such devices are not only expensive to manufacture but difficult to clean and sterilize for each use. Such continuous flow systems are shown in U.S. Pat. Nos. 3,489,145; 3,519,201; and 3,655,123.
Given these cost and operational problems, systems have evolved using bag structures which do not require a channel directly receiving the fluid to be separated. Such systems are shown in U.S. Pat. Nos. 3,748,101 and 4,007,871.
U.S. Pat. No. 4,278,202 relates to a centrifugal system having a flow path that increases in cross-sectional area from inlet to outlet. The increase in area occurs by diverging spirals of the side walls as well as increasing the depth of the channel. The separation container is made to correspond to this channel configuration and employs an internal fluid connection for the input running along the inner circumferential length of the container. The entire channel is inclined to the rotor axis at an acute angle. Such a device is difficult to manufacture given the geometry and the container is expensive to make on a mass production basis. Also, the geometry of the system makes it difficult to collect fractions in the buffy coat given the lack of a stable collection chamber. The patent perceives only collection of the most dense and the least dense fractions with the output portions as shown.
Reference is made to U.S. Pat. No. 4,094,461 which discloses a disposable centrifuge bag placed between the inner wall of the centrifuge bowl and a filler or centerpiece. The '461 patent represents a significant advance in the prior art by defining not only a disposable centrifuge bag but also a collection region which acts in a self-regulating manner. While the subject matter of the '461 patent has found widespread practical application, there still remain a number of areas for improvement.
First, a standing requirement in extra-ventricular systems of the type defined by the prior art is to reduce the volume of blood which is processed outside of the body. Reducing the blood volume requirements of the separation system allows the procedure to be tolerable for a wider range of donors. For example, physically smaller donors having a less than "normal" blood volume themselves cannot tolerate a procedure that requires their limited blood volume to be extra corporeal. Also, a reduction insures that during such procedures, donors will not be unduly deprived of cells that have not been collected. Those sick donors having specific needs for certain types of cells, such as a chronic anemic requiring red cells, cannot accept short term losses. Hence, it is desirable to define a system having minimum extravascular volume requirements that still retains separation and collection efficiently at existing levels.
A second requirement in such continuous flow blood centrifuge systems is to define a device capable of automatic priming (filling) and complete emptying of the container. At the beginning of each run prior to establishing the blood flow, air must be first expelled from the container and the device primed with a sterile solution as saline. Current systems require operator control for this initial step such that procedures are operator intensive in a field where skill levels among individuals are difficult to maintain at acceptable standards. At the end of each procedure, the container must be emptied of all red cells which remain. This is conventionally done also by operator control using the introduction of saline into the chamber which itself displaces packed red cells from the chamber into the collection zone where they can be returned to the donor.
It is implicit that such systems must be maintained sterile and capable of easy cleaning to achieve sterility in the blood handling equipment. Moreover, separation of the blood fractions must be conducted in a manner that does not injure or destroy blood cells. Cell fragility is an important facet in evaluating the overall efficacy of any system.
Accordingly, while the prior art evidences significant advances in continuous flow blood centrifugation systems, areas of safety, efficiency, and automation remain for continued development. Given the stringent safety requirements implicit in any in vivo blood handling system, improvements in collection efficiency and operation must be made without compromising the overall efficacy of the procedure. Accordingly, techniques which may attempt to achieve higher levels of efficiency are fundamentally untenable if they have a propensity for reducing any paramount safety criteria of such systems, such as criteria of sterility and blood fragility.